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Re: Thermal generating

PostPosted: Tue Apr 17, 2012 7:15 am
by Rick Masters
I found myself in a gaggle of sailplanes once in an Aolus, back in the early 80s off the Whites of Owens Valley.
The Aolus was unlike any glider I have ever flown in that you could aggressively yaw it into a flat spin in a thermal core by holding your body parallel to the trapeze and pushing off to the side, hanging as much of your weight as you could under the inside-turning wing, using the drag of your body like a rudder at full stop, and holding your weight quite a bit aft - aft of what was usually the stall point. The glider would slow down to a eerie zone of almost dead silence and you would experience a floating, bobbing sensation as you hung on the weighted side, suspended on the verge of a tip stall . If you tried this in normal air, you would be diving in a milisecond. But the Aolus, because of its unusual tail, had an amazing quality of becoming stable in such a yaw-induced flat spin within a strong thermal core. I will never forget the way the sailplanes circling around me fell away below. They fell away FAST! To this day, I don't believe anything the same size can touch a flat-spinning Aolus in a thermal core.

The designer of the Aolus, Carlos Miralles, taught me to dive-bomb my chosen cross-country out-landing zone by making a fast, low pass to break free any nascent thermals, then circle around and land. Not only did this make for a safer landing, but on several occasions I found thermals as I returned on final and rode them up to the crest from the valley floor. I would recommend this technique as a primary survival tactic in desert landings.

Later in the 80s, I developed a better method of retaining my position in the thermal core by using Alan Fisher's Thermal Snooper.

Re: Thermal generating

PostPosted: Thu Apr 19, 2012 9:31 pm
by Bill Cummings
Terry, Terry (my wife--here we go again--) once bought some sunglasses from a store in Chelan, Washington. It wasn’t long before I noticed that she was pointing out thermals/dust devils as we were heading back to the lake after a day of flying that I couldn’t see.

Finally in exasperation I had her pull over and had her point out the dust devil that she could see that I could not.

While pointing out the dust devil she pulled her sunglasses down to the end of her nose, looked over the top of them and said, “Hey! Where did it go?” She then put the sunglasses back on and said, “Hey! These sunglasses are “Devil Glasses!” :o She handed them to me and I put them on and I could finally see the faint dust devil that was not apparent to the naked eye as the devil moved against the blue sky in the background. :shock: They may have been polarized sunglasses but I’m not sure. My attempts to keep the sunglasses (I mean if she really loved me of course-- :cry: ) came up short. :oops: I had to go to the same store and buy my own pair. :evil:

The only trouble with them was that from the air, with a dirt field for a background, I was unable to see the faint dust devils below me. :thumbdown:

The best way, for whichever of us was driving that day, was to radio up to the pilot which direction from the van the dust devil was and the person flying would search in that direction. :thumbup:

We agreed that the 12 o’clock position would always be right in front of the vehicle and of course 6 o’clock would be behind the vehicle. We would radio up the position of the clock that the thermal was from the van to lead the pilot into it.

I had notice while in Viet Nam that the military issue prescription sunglasses, that had a neutral gray shade, would make Olive Drab fatigues (Clothes) stand out from the green shade of the jungle vegetation.

Without the sunglasses the clothing would blend in with the vegetation and make for a seriously scary camouflage situation. :shifty:

(Side note: Following a car in a snow storm with either set of glasses would make the car ahead visible where taking them off would only reveal the swirling snow behind the vehicle.)

Maybe the shade, polarization, both, or something else was causing this ----anomaly. Anyway, just something else we put in our bag of tricks for thermal flying.

My best discovery ever was flying with my Garmin GPS, in “Track Up,” mode with a fast recording crumb trail. It would show the thermal I was circling in on its screen like a tilted coil spring. When ever I would loose the thermal due to a reason like camera, radio, peeing, sightseeing, map reading, I would just look for my coil spring track on the screen and if it was lower left I knew that my lost thermal was in back of me and to my left.

As I turned to go back to it the coiled spring image on the screen the image would swing around to a position in front of me at the top of the screen. I would then lead it to the downwind side since it would be moving/blown down wind.

Ninety nine times out of one hundred the thermal was still where I left it and it had not fizzled out.

Re: Thermal generating

PostPosted: Mon Apr 23, 2012 10:54 am
by Bob Kuczewski
Great posts Rick and Bill!!    :thumbup: :thumbup: :thumbup:

billcummings wrote:Ninety nine times out of one hundred the thermal was still where I left it and it had not fizzled out.

I've often wondered how many times I've thought that a thermal had "fizzled out" when really I had simply failed to track it properly. Ninety nine out of one hundred means I need to work harder!! ;)

Re: Thermal generating

PostPosted: Tue Mar 15, 2016 11:42 am
by Bill Cummings
billcummings wrote:Terry, and Hawks,
Having a good deal of flying from boat towing and later flying over the wheat fields of Washington State this is what I have noticed that many other pilots may not yet have made this same discovery.

When a thermal, dust devil, leaves a bare field of dirt and enters a wheat field many times the thermal will not pick up enough dust to continue to mark itself.

The foot print of the thermal can be tracked, or seen, by following the lighter shade of wheat as the thermal swirls it’s way downwind. It looks like a bright spotlight moving and swirling across the wheat field.

Just the opposite happens when a thermal moves out over a body of water. The foot print of the thermal looks darker than the surrounding water. This dark wind print over water can be seen from many thousands of feet above whereas leaves fluttering as the thermal moves across the top of a grove of trees cannot be seen from much more than about a thousand feet above.

For new pilots trying to enter these thermals, that can be seen leaving a footprint on the ground, I tell them to lead the thermal to the downwind side. If they ask me, by how much they should lead the thermal to intersect it I tell them this:
Stand up and move one of your hands about a foot away from your leg. That is the angle to be downwind of the thermals foot print on the ground. Strong wind days it will of course need a greater angle. This is just a starting reference point for them.

Just like putting some “English” (spin) on a ping pong ball, tennis ball, or baseball a person can make the path of the ball curve or tack off of the direction the ball was thrown. (Oh yes, you can be seated and finish reading now.)

The same thing happens as a spinning thermal is being blown downwind.

The thermal will not blow straight downwind but tack off to the left or the right of the winds course line depending on the thermals rotation (spin/“English”).
This will also make the thermal lean to the left or right as it tacks its way slightly off of the downwind course line.

So If you are flying downwind to the next thermal and the foot print or dust near the ground gives you an indication of which way the thermal is rotating, clockwise or counter clockwise, this will tell you which way left or right of the footprint you need to fly to intersect the leaning invisible thermal at your altitude.

Darn it! ---- :oops: I’ve got to get out more! :? I used to know which way to search for the thermal above its footprint as it moved downwind depending on its rotation and now I can’t remember! :oops: :oops:
I guess you will have to sort this out yourselves.
Let’s see now ---if a ping pong ball has right “English” on it and it curves left---then a thermal blowing down wind would go------???? :?:
Darn it!
Oh well! It was a lot of fun back when I figured it out for myself so I wouldn’t want to spoil the fun for everyone else.

At this later date I did some research on The Magnus Effect. Maybe Bob K. with his wind tunnel knowledge can keep us on the straight and narrow path of correctitude. (New word by the way --one of mine as far as I know.)
The Magnus effect link below has to do with solids I think and not what I'm really trying to find which is how wind effects thermals.
Maybe this analogy (The Magnus Effect) isn't properly applied but it gives a visual representation the effect the wind has on thermals even if it is not scientifically correct. (For that I'll need some help.)

In the last part of the quote above I talked about thermals tacking off to one side or the other, depending on the rotation, and not following the exact same wind direction.
I also talked about the thermal leaning left or right as it moves downwind in relation to it's visible footprint (dust devil) on the ground. This is also the result of the direction of rotation.
After reviewing the video it now makes sense to me what the answer is to the question I left the readers hanging with in the quote above.

It now makes sense to me that as a pilot overtakes a thermal moving downwind the pilot should see what the rotational direction is.
If the direction is clockwise expect the invisible thermal at the pilots altitude to (more likely than not) be to the left and downwind of the dust devil on the ground. Just the opposite for a counterclockwise rotation.
Magnus Effect.PNG
Magnus Effect.PNG (205.12 KiB) Viewed 4824 times

Re: Thermal generating

PostPosted: Thu Mar 17, 2016 11:43 pm
by Bob Kuczewski
The basketball drop off the top of the dam was really really amazing!!!

Thanks for posting this!!!      :thumbup: :thumbup: :thumbup: :thumbup: :thumbup:

Re: Thermal generating and spotting.

PostPosted: Tue Mar 22, 2016 7:25 pm
by Bill Cummings
The Northern Sky Gliders Club out of Minneapolis/St. Paul, Minnesota would fly the cliffs on each side of Lake Pepin. Due to the locks and dams down river, Lake Pepin was really a wide spot in the river by about a mile. While soaring the 375' to 400' cliffs the pilots would look for wind prints on the surface of the lake. When the gust prints would converge into a "V" shape the locals there called them, "Slams."
At the sharp end of the "V" was where the lift (thermal) was. The pilots would fly upwind out of the ridge lift to get above and slightly downwind of the incoming Slam, (thermal). They then would circle all the way back toward the ridge lift and once there that would add to their climb rate.
I imagine they named them Slams instead of thermals after having read material from Dennis Pagan. Material by the way that turned out for a long time to be this water tow pilots biggest anchor until I learned better. :shh:
The surface convergence wind print was reduced immediately downwind of the Slam.

I speculate the thermal was drawing air into itself which reduced the wind speed on the surface thus less lake surface disturbance downwind of the slam.
NSG pilots Larry Smith, Greg Ballentine (sp?), pointed this trick out to me some thirty plus years ago. :thumbup:

Re: Thermal generating in snow country,

PostPosted: Fri Apr 01, 2016 9:35 am
by Bill Cummings
Thermals in snow country,
During the Northeastern Minnesota winter just before Spring and around Lake Superior (one of the five US inland "Great Lakes,") there was an abundance of "Lake Effect Snow."
The Great Lakes many times don't freeze over all winter. The moisture given off by Lake Superior would end up becoming snow for up to 50 to 80 miles inland from Lake Superior.
Depending on the wind speed and direction this extra snow fall could stretch one hundred miles or more from the lake.
Towing on the frozen lakes inside of this snow-belt became tougher to do when we were down wind of areas that were losing snow cover.
We would pack up and drive many miles with our snowmobiles (on trailers) to the frozen lakes with areas of fifty percent snow cover on the ground surrounding the smaller inland lakes.
One lake we favored had a large hill to the west where a town was located on the south side of the hill.
This southern facing hill would be free of snow but everywhere else still had 50% snow cover. We would tow up on the frozen lake ice and fly out over the bare ground near the town site.
There were times when one snowmobile would eventually have 3 to 4 hang gliders up thermaling over town at the same time.
One might think that an area with 50% snow covered ground would not be good for producing good thermals but just the opposite is true. It was easier to thermal at that time of year than when all the snow was gone.
It would be my best guess that spotted 50% snow covered and uncovered ground made well defined areas of instability for the air we were flying in.

Re: Thermal generating

PostPosted: Fri Apr 01, 2016 10:16 am
by Rick Masters
Dust devil trails on Mars.
The Martian dust devils range up to 8 km high.
They pick up the lighter sand and leave the darker, heavier sand.
I've thermaled the tops of dust devils half that high on Earth.

Re: Thermal generating

PostPosted: Wed Apr 20, 2016 1:26 pm
by Bill Cummings
I don't know if while asleep I had a dream about this or somewhere in my past I read about it.
Sailplanes would fly out over a field and on the ground people would open louvers, suspended above the ground, like window blinds, to release the heated air. Instead of the blinds being hung vertically they would be horizontal to the ground.
So whether or not they actually do this somewhere in the world for generating thermals for sailplanes, how would one go about doing this?
(Maybe a Google Search?)
Would you want clear louvers (is that spelled right?) above dark ground?
How high above the ground would be optimal?
How big of a surface area would one need?
Would a small area be enough of a triggering mechanization that would siphon warm air from along the ground out beyond the louvered area?
Might a pilot by means of radio remote control activate the louvers open and closed?
Could this be done cost effectively?
Could this be done with some other idea that was better than louvers?
How about over a volcanic vent?
How about over a power plant water cooling pond?
How about grass fires?
How about over the, "Burning Man Fire?" (Once a year.)
Any other ideas :?:

Re: Thermal generating

PostPosted: Wed Apr 20, 2016 2:47 pm
by JoeF
LIFT ezine had a page on topic:
Artificial Thermals
Black bodies and black surfaces
Heat of compression
Ambient temperature of air mass
Opportunities on cold days
Opportunities on calm wind days
Opportunities in directing wind
Geothermal opportunities
Hot-house opportunities
Clear-glass shrouding
Clear-plastic shrouding
Hot spring opportunities
Structured nations where serial artificial thermals allow dependable transport of goods and people
Kite energy systems using energy to heat captured air for cycled release to give thermal for HG
Solar-energy farms
Roofing decisions
Sectored raised encapsulations with triggered opening of the covers
Designer thermals
Timed thermals
Triggering thermals
Thermal measuring
Thermal visualization
Thermal classification
Tumbling in thermals. Tumbling mitigation.
Economics of artificial thermals
Thermal shaping
Pulsed thermals
Thermal texturing
Thermal separation engineering
Electrical measures of the thermal environment
Role of water in artificial thermal engineering (liquid, vapor, steam, humidity, air conditioning, ...)
Giving odors to artificial thermals
Giving treatments to thermals to provide certain kinds of thermal visualization (natural visible or special types of instruments)
Vertical velocities of artificial thermals
Flatland long vent
Long sequenced venting
White and black
Ocean-city black roof